A) Field of the Invention
The present invention relates to a solid state imaging device, and more particularly to a packaged solid state imaging device and a manufacture method thereof.
B) Description of the Related Art
FIG. 5A is a block diagram showing the main part of a solid state imaging apparatus and FIG. 5B is a schematic plan view showing the configuration of a solid state imaging device.
As shown in FIG. 5A, the solid state imaging apparatus is constituted of: a solid state imaging device 51; a drive signal generator 52, an output signal processor 53; a storage 54; a display 55; a transmitter 56; and a television 57. The solid state imaging device 51 generates signal charges corresponding in amount to the amount of incident light upon each pixel and supplies an image signal corresponding to the generated signal charges. The drive signal generator 52 generates a drive signal (transfer voltage and the like) for driving the solid state imaging device 51 and supplies it to the solid state imaging device 51. The output signal processor 53 processes the image signal supplied from the solid state imaging device 51 to perform noise reduction, white balance, data compression and the like. The storage 54 is connected to the output signal processor 53 and stores the image signal. The storage 54 may be a memory card. The display 55 displays the image signal and may be a liquid crystal display. The transmitter 56 transmits the image signal to an external. The television 57 displays the image signal when necessary.
Solid state imaging devices are generally classified into a CCD type and a MOS type. The CCD type transfers charges generated in pixels by CCDs. The MOS type amplifies charges generated in pixels by MOS transistors and then outputs an image signal. In the following, the CCD type is used by way of example and not restrictively.
Signals to be supplied from the drive signal generator 52 to the solid state imaging device 51 include a horizontal CCD drive signal, a vertical CCD drive signal, an output amplifier drive signal and a substrate bias signal.
As shown in FIG. 5B, the solid state imaging device is constituted of: a plurality of photosensors 62 disposed, for example, in rows and columns; a plurality of vertical charge coupled devices (VCCDs) 64; a horizontal charge coupled device (HCCD) 66 electrically coupled to vertical CCDs 64; a drive circuit (and wirings) 65 for driving CCDs; and an amplifier (floating diffusion) 67 disposed at the end of the horizontal CCD 66 for converting an output charge signal into voltage. A pixel arranged area 61 includes the photosensors 62 and vertical CCDs 64.
Each photosensor 62 is a photoelectric conversion element. The photoelectric conversion element generates and accumulates signal charges corresponding in amount to an incident light amount. The accumulated signal charges are read to the vertical CCD 64, and transferred in the vertical CCD 64 toward the horizontal CCD 66 in the vertical direction. The vertical CCD 64 transfers signal charges in response to a transfer voltage (drive signal) supplied from the drive circuit 65. The signal charges transferred to the end of the vertical CCD 64 are transferred in the horizontal CCD (horizontal transfer channel) 66, converted into voltage by the amplifier 67 and output to an external.
FIG. 6A is a plan view showing the outline of a partial area of the pixel arranged area 61 of the solid state imaging device, and FIG. 6B is a cross sectional view taken along line 6B—6B shown in FIG. 6A. For the simplicity of drawing, some constituent elements shown in FIG. 6B are omitted in FIG. 6A.
As shown in FIG. 6A, a vertical transfer channel 73 is disposed between photosensors 62 adjacent in the horizontal direction. A first-layer polysilicon transfer electrode 71 and a second-layer polysilicon transfer electrode 72 are disposed covering the channels 73, and overlapped at their one ends along the channel longitudinal direction. Both the polysilicon transfer electrodes extend generally along the direction perpendicular to the longitudinal direction of the vertical transfer channel 73. The transfer electrodes made of two stacked electrode layers occupy the smaller areas between photosensors adjacent in the vertical direction. For example, four-phase drive signals (transfer voltages) are applied to a unit of four or eight transfer electrodes 71, 72, 71, 72 to transfer signal charges generated in the photosensors 62 in the vertical transfer channel 73.
As shown in FIG. 6B, an n-type charge accumulation region 62 constituting the photosensor and the adjacent n-type vertical transfer channel 73 are disposed in a p-type well 82 formed in a semiconductor substrate 81 of, for example, an n-type. The first-layer polysilicon transfer electrode 71 is formed on an insulating layer 74 above the vertical transfer channel 73. After an insulating layer such as a thermally oxidized film is formed covering the first-layer polysilicon electrode, the second-layer polysilicon transfer electrode 72 is formed overlapping the first polysilicon transfer electrode 71 at their end portions. The surface of the second-layer transfer electrode is also electrically insulated by a thermally oxidized film or the like. The first-layer and second-layer transfer electrodes are alternately disposed along the longitudinal direction of the vertical transfer channels. The vertical CCD 64 is constituted of the vertical transfer channel 73 and upper level insulating film 74, first-layer transfer electrode 71 and second-layer transfer electrode 72.
The n-type transfer channel 73 and p-type well 82 form a pn junction so that when light becomes incident thereon, pairs of electrons and holes are formed and noises are generated. In order not to make light incident on an area other than the photosensors, a light shielding film 83 having openings above the photosensors and made of tungsten or the like covers the first and second polysilicon electrodes. At this stage of manufacture, only the insulating layer 74 exists above the light receiving area of the charge accumulation region 62. Stacked above the vertical channel 73 are the insulating layer 74, first and/or second silicon electrodes 71 and 72 (having overlapped areas between pixels adjacent in the vertical direction and at end portions of the transfer electrodes above the vertical channel), and light shielding film 83. At this stage of manufacture, the uppermost surface has the curved surface increasing its height from the substrate surface toward the outside area of the light receiving area.
Signal charges generated in the photosensor 62 corresponding in amount to the incident light amount are read to the vertical transfer channel 73 in response to a read voltage applied to the first-layer transfer electrode 71, and thereafter transferred in the vertical transfer channel 73 in response to the transfer signal (transfer voltage) applied to each of the first-layer and second-layer transfer electrodes 71 and 72. The shielding film 83 with openings above the photosensors 62 prevents light incident upon the pixel arranged area from becoming incident upon the area other than the photosensors 62.
Three primary color filters 84 of red (R), green (G) and blue (B) are formed on an insulating layer 105 made of, for example, silicon oxide (SiO). On the color filters 84, micro lenses 85 made of, for example, photoresist, are formed. The micro lens 85 is disposed above each photosensor 62 and is, for example, a semispherical fine convex lens. For example, the refractive index of the micro lens 85 is 1.6 to 1.7. The micro lens 85 converges incident light at the photosensor 62. Light converged by the micro lens 85 passes through the corresponding one of the three primary color filters 84 and becomes incident upon the photosensor 62. In this specification, the structure having the light shielding film 83, insulating layer 105 and color filters 84 above the photosensor 62 and vertical CCD 64 and having also a function of supporting the micro lenses 85, is called a micro lens support layer 106 where appropriate.